Electric line fault locators



Nov. 29, 1955 T. w. STRINGFIELD Erm. 2,725,526

ELECTRIC LINE FAULT LOCATORS Original Filed March 3l, 1949 3Sheets-Sheet 3 Hl f L+ /P/CHARD E STEVEN WARREN V. BEHRENS of America asrepresented by the Secretary of the Department of the Interior Originalapplication March 31, 1949, Serial No. 84,666,

now Patent No. 2,628,267, dated Feb. 10, 1953. Divided and thisapplication ctober 2, 1952, Serial No. 313,618

11 Cls. (Cl. 324-52) (Granted under Title 35, U. S. Code (1952), sec.266) This invention relates to the operation of electric powertransmission lines.

This application is a division of application Serial No. 84,666, filedMarch 31, 1949, now Patent No. 2,628,267, issued February l0, 1953,entitled Electric Line Fault Locators by Theodore W. Stringeld, Lyman R.Spaulding, Richard F. Stevens, and Warren V. Behrens.

In the practical operation of transmission lines, faults occuroccasionally as the result of broken insulators, ilash-overs due tolightning strokes or other causes. Faults are characterized by failureof insulation or dielectric between a line conductor and the ground orbetween two or more line conductors.

Many faults involve only a temporary breakdown of the dielectricinsulation between conductors and ground (ashover and are) and cease toexist after the line is de-energized, allowing the line to bere-energized mmediately. However, in many cases the insulation is leftin a damaged condition necessitating repair to prevent successivefailures. The damage may also be such as to decrease the ashover valueof the insulation below normal line voltage preventing re-energizationbut such as to retain so high a resistance that the line appearsunfaulted to lower voltages Which might'be used for test. Exceptionallysevere faults may cause complete destruction of the insulation, possiblydropping the conductor, and the D.C. resistance of the fault may be ofalmost any value depending upon the extent of the damage.

This invention has as its principal object the location of transmissionline faults at the time the fault occurs by remote observation of thetransmitted effects or evidences of the fault. Another object is to makea record of the occurrence of the fault from which the location can bedetermined at any subsequent time. Still another object is to provide avisual indication of the fault location immediately after itsoccurrence. Another object is to provide arrangements for making thefault location record photographically with a minimum of manualoperations. Other objects include the transmission of the fault-locatingsignals by radio apparatus and the use of a recording meter as adistance indicator. constitutes this invention is described in thespecification and drawings following and succinctly dened in theappended claims.

The specification has reference to the drawings in which the respectivenumerals indicate equivalent entities in the several drawings wherein:

Figure 1 is a schematic diagram of this invention in a preferred formutilizing direct transmission line propagation of fault signaltransmission.

Figure 2 is a similar diagram showing the invention for use with radiotransmission of fault signals.

Figure 3 is a circuit diagram of a novel linear sweep and voltage storerwhich is a component of the system shown in Figure 2.

Figure 4 is a circuit diagram showing in some detail arent portional tothe pulse magnitude.

the principal components of the system embodied in Figure 1.

in Figure 1 there is shown in one-line convention a power transmissionline embodying the principles of our invention. Several of theindividual components of the system are indicated by labeled blocks. Ineach instance the labeled block within itself can be derived fromconventional apparatus. It is the novel combination and use of theseconventional components that is involved in this embodiment.

The transmission line tions subdivided for in Figure l, composed of twosecpurposes of explanation into partial lengths 1, 2, and 3, issubjected to a fault arcover 4. Ordinarily the line would be polyphasebut throughout Figure 1, the one-line convention is used forconvenience. Associated with the transmission line there are, for thisillustration, three substation busses 5, 6, and 7.

A capacitive or other suitable coupling 8 is placed in operativerelationship with bus 5 so that any change in voltage occurring betweenline and ground on bus 5 impresses a corresponding difference ofpotential on coupling S. Coupling 8 is connected to a signal line 9,such as a coaxial cable through a resistor 11. The combination of thecoupling S, signal line 9 and resistor 11 acts as a socalleddifferentiating circuit or high-pa-ss filter, passing only the steeplyfronted component of a traveling wave, and delivering under suitableconditions sharp pulses of short duration through signal line 9.

Signal line 9 is connected to a second resistor 13 which terminates theline in its characteristic or surge impedance. That is, the value inohms of resi-Stor 13 is numerically equivalent to the surge impedance ofline 9. The output of signal line 9 is impressed upon a pulse amplier14. Pulse amplifier 14 delivers an amplified pulse signal to a phasesplitter 15.

The phase splitter 15 is capable of receiving pulses representingpotential differences which are either positive or negative with respectto ground and delivering therefrom two pulses, one of which is positiveand the other negative with respect to ground. These positive andnegative pulses are delivered by phase splitter 15 to a full waverectifier 16 which rectifies the received pulses delivering a singlepulse polarized in a selected direction. Thus, regardless of thepolarity of the pulse of potential diierence received at coupling 5,`the polarity of the pulse delivered by rectier 16 is always the same.

The pulse output of rectifier 16 is delivered into two separate paths,one of which, beginning with a pulse amplier 17, operates as a signalamplitude transmission path; and the other, beginning with an inverteramplifier 18, operates as a timing or triggering channel.

Pulse amplifier 17 transmits a signal to a cathode follower 19 whichoverdrives a remote cut-oli type vacuum tube in a signal biasedamplifier 2i) in which a grid leak bias is set in accordance with themagnitude of the first pulse received in a sequence or operations. Thegain of amplifier 2@ is, by this process, set to values inversely pro-The gain, once set, remains approximately constant for a length of timesui-"- cient for completing the operation of the system. The output ofsignal-biased amplifier 20 is delivered to an inverter amplifier 21where the signal is further amplified and inverted. The inverted signalis delivered to the vertical (Y) axis amplier of a cathode-rayoscilloscope 22 which provides the necessary difference of potential forthe vertical deflection of the oscilloscope trace.

In the second signal path, beginning with inverter amplifier 18, theamplified and inverted signal is delivered to a thyratron switch 23which is ionized into conductivity by the received signal. A voltageproduced in the cathode circuit of tube 23 is used to trigger the sweepcontrol circuit of the oscilloscope 22. The oscilloscope is arranged tosweep the cathode ray or trace once across the horizontal (X) axis ofthe oscilloscope for each triggering irnpulse. After each operation,tube 23 is extinguished and reset by a reset tube 25` which operatesrelay 26, mornentarily interrupting the plate current to tube 23.

Switch tube 23 when ignited causes a current to ow in the coil of asolenoid 27, the aramture of which strikes a button 2S on a camera 29causing a new frame to rack up after the phenomena traced inoscilloscope 22 has been photographically recorded. Camera 29 is aconventional moving picture camera mechanically arranged with a lightshield 31 to photograph the cathode ray trace appearing in theoscilloscope tube 32 of oscilloscope 22. Light shield 31 is providedwith a peep opening 33 to permit adjustment of the system by theoperator.

An arrangement for recording the time of each photograph is provided inan. extension 34 of the light shield 31 in which an argon lamp isplaced. A clock or watch of conventional form. is illuminated each timea current impulse is produced by switch tube 23. The momentaryillumination of the clock impresses the clock image on the film. framethen in exposure in camera 29 providing a record of the time of theoperation of tube 23.

The successive frames of film in camera 29 are in exposure for varyinglengths of time. If no fault occurred, the film frame would remainindefinitely. There is a small amount of light from the glow of thecathode in the cathode ray tube 32 which gradually fogs the exposed filmframe. This effect may be decreased by interposing a light filter 37between the camera 29 and light shield 31. The film frame is advancedperiodically by a synchronously driven triggering contactor 3S.Ordinarily the film is advanced once each hour.

The structure described above is composed of components whichindividually can be found in the literature of the related arts,particularly radar. The modifications required in existing devices toadapt them to use in our invention are of a type that could ordinarilybe accomplished by one suiciently skilled in the related arts.

For explaining the overall` operation of this invention for the locationof transmission line faults, let it be assumed that a fault. such as aflashover from line to ground occurs at 4 as indicated. When thisashover occurs, a surge of voltage and current is propagated along thetransmission line portions 1 and 2 in both directions from the fault.The propagation of. the surge from the fault 4 to the bus follows acourse indicated by the dotted line 41. The surge from fault 4 to bus 6follows a course 42.

The arrival of the surge at bus 5 results in impressing a difference ofpotential on collector 8 which is transmit ted and amplified throughline 9, etc. to the oscilloscope 22, triggering the X-axis oscilloscopesweep. This surgev is then partially reliected from bus 5 back towardfault 4 where it is again reected back to bus 5 where it arrives for thesecond time. The difference in time between these two successivearrivals is proportional to twice the distance between bus 5 and fault4.

The surge from fault 4 to bus 6 is reected at bus 6 back to bus 5,arriving at bus 5 after the surge that traveled directly from 4 to 5.The difference in time between the arrival of the surge reflected frombus 6 and the surge arriving at bus 5 directly from fault 4 isproportional to the difference between the distance from 4 to 6 and backto 5, and the distance from 4 to 5, this difference being equal to twicethe distance between 4 and 6. The time taken by the cathode ray tube 32sweep along the X-axis is adjusted to be more than the maximum possibledifference in time between the arrivaly of the surge directly from 4 to5 and the arrival of the surge by reection from bus 6. This length oftime is approximately twice the length of the line section bus 5 to bus6 divided by the speed of surge propagation along the line which speedis only a little less thany the speed of light.

The duration of time to which the X-axis sweep is adjustedv ispreferably limited to the time required for the surge to travel twicethe length of the line section bus 5 to bus 6, in order to obtain themaximum expansion of scale in the sweep length available on the face ofthe oscilloscope tube. If additio-nal lines of shorter length than 5 to6 also terminate at bus 5, then reection from the far terminals of theselines will also appear in the record and are identified by knowledge' ofthe lengths of the corresponding lines.

Thel record of the surges is made in the form of brief deection of thecathode ray tube beam in the Y-ax'i'sA direction along the' X-axis.These deflections are Commonly referred to as pips as in radartechnique. In oscilloscope 22, a conventional timing circuit providescalid brated marker pulses which are also fed to the Yaxis deectionplates in tube 32 with such polarity as to produce small downward pipsat intervals corresponding to selected distances such as l0 miles oftransmission line. The circuit through rectifier 16 is connected so thatthe fault surge pips produce upward deflection. The record isinterpreted by observing the distance between the trace origin and thesurge pips in miles of line.

Ordinarily the record will show two pips which are desired forinterpretation. One pip will be that` recorded when the fault surge hasarrived at bus 5 after having traveled from fault 4' over the firstthird of path. 41 toA bus 5,v then having been. reflected at bus 5,traveling back to fault 4 over the second third of path 41 and therebeing. reflected again, and finally traveling a second time over thethird of. path 41 to bus 5 at which time the arrival would be recorded.It has already been explainedy that the first arrival ofthe fault surgeat bus 5 from fault 4 was used to trigger the sweep operation of therecording equipment. The second desired pip will be that recorded afterthe fault surge has traveled from fault 4 to bus 6 over the first partof path 42 where reflection would occur, and back over the remainder ofpath 42 through fault 4 to bus 5.

Ambiguity exists in the identities of pips resulting4 from the surgesreceived over the respective paths 41 and 42. The fault location,however, is known immediately to be in one ofy either of two placesequally distant from bus S and bust 6 respectively. That is, forexample, a fault 10 miles from bus 5' will under some circumstances makea record which by simple measurement only would not be distinguishedfrom a fault 10 miles from bus 6. This ambiguity is, in effect,eliminated inasmuch as the pips are of varying shapes. The pips producedby reection at the busses where the coetiicients of reflection of thesurges are more favorable are sharper and of greater magnitude then pipsproduced by less favorable reection at the fault. Thus an operator isable to interpret the record correctly.

The necessity of using an oscilloscope and photographic recording havebeen avoided in a second pre ferred form of embodiment of our inventionas shown in Figure 2`. In- Figure 2, those components of the systembearing numerals the same in Figure 1, operate as already described.O'mitting other parts of Figure 1, Figure 2 includes means fortransmitting a surge signal from the end` bus 7 of the line to bus 5 bya radio channel which in a preferred form approximately parallels theline and utilizes either short wave radio or carrier current transdmission.

Specifically in Figure 2, elements 8 to 16 inclusive operate withamplifier' 18, and switch tube 23' to provide a triggering' signal to'initiate action in a time recording system which receives, in effect, a'single impulse from bus 5 and one from bus 7. For this purpose, theoutput signal of. switch tube isV delivered to an electronic counter 51of ordinary commercial form and a nip-flop multivibrator 525. Electroniccounter 51 and multivibrator 52 receive also impulses from a secondswitch` tube 53 which is actuated by the detected signal from areceiverr 54. Receiver 54 is conventional, receiving a radio signalthrough an antenna 55. Flip-lop multivibrator 52- starts= a linear sweepand voltage storer 56` (explained in detail in reference to Figure 3)which delivers a voltage to a recording or maximum reading voltmeter 57.Multivibrator 52 starts voltage storer 56 on the first impulse of acycle and stops storer Sti on the succeeding impulse. Voltage storer 56produces and stores a voltage proportional to the time between theinitiating and stopping impulses.

The surge signal that stops electronic counter 51 and voltage storer 56arrives from the distant end of the transmission line. At bus 7 acoupling 5S, resistor 61, pulse amplier ed, phase splitter 65, and fullwave rectifier 66 perform functions exactly similar to those of elements8 to i6 inclusive atbus S. Full wave rectifier 66 delivers a pulsealways of the same polarity to a pulse modulator 67 which modulates aradio transmitter 63 sending out signals on antenna 69. The transmittedradio signals from antenna 69 are received in the conventional way byantenna S5.

In the system of Figure 2, a fault l produces a surge that reaches bus:"5 in time equal to the distance fault 4 to bus 5 divided by a velocitya little less than the speed of light. A surge originating at fault 4travels also in the line toward bus 7 where a signal is Vsent by radioto antenna 5S which is near bus 5, so that the bus-7 pulse arrives ineffect at bus 5 in time equal to the distance fault 4 to bus 7 dividedby a Velocity a little less than the speed of light plus the distancefrom bus 7 to bus 5 di vided by the speed of light. A fault 4 occurringat bus 7 would be signaled at bus 5 by radio almost simultaneously butslightly ahead of the pulse received at bus 5 from the transmissionline, depending on the actual transmission line distance as compared toair line distance, so the operation would be defective. This is avoidedby introducing a conventional signal delay line 7l into the circuit andshown for convenience between resistor 61 and amplifier 64 so that anyfault, wherever it occurs on the line sections l and 3, will arrive atbus 5 over the line before it can arrive at bus 5 by radio. The requiredtime of delay is determined and adjusted for the particularinstallation.

In interpreting the records of faults in the electronic counter 5l andthe recording voltmeter 57, the recorded time is the difference betweenthe time of arrival of the fault pulse by way of bus 5 and the time ofarrival of the fault pulse by way of bus `7. rl`he time difference isrelated to line length and fault location by calibration providinganalytic, graphical, or tabular relationships as may be desired forrapid conversion to distance upon occurrence of a fault. The scales ofthe electronic counter 5l and recording voltmeter 57 can be calibratedto read direct in miles distance of the fault from a specitied locationon the line sectiony l and 3, as from bus in Figure 2 all the labeledblocks represent instrumentalities which can be of conventional form orof a form that could be derived from conventional forms by modificationsthat could ordinarily be expected to be accomplished through design byone thoroughly skilled in the related arts. An exception is the linearsweep and voltage storer 56. This is explained further in reference toFigure 3.

in Figure 3, a triode vacuum tube 8l receives the flipop signal from theflip-op multivibrator 52 applied to the control grid of tube Sl. Tube elnormally is in a condition of zero bias so the plate is virtually atground potential. When the first signal to the flip-dop is received,bias voltage is developed on the control grid of tube 3l so a voltage isbuilt up between the plate and cathode thereof. This voltage is appliedto a condenser S2 through a diode d3.' Condenser 82 receives a charge ata rate proportional to the quotient of voltage of tube 8l minus thecondenser voltage divided by the resultant resistance of a resistor 84in the circuit of condenser 82, and other circuit elements associatedtherewith. This proportionality of rate of charging departs fromlinearity if no compensation is applied.

Compensation to produce linearity is accomplished by using a secondtriode with a cathode resistor 86 and a connection to the plate circuitof tube 81 through a condenser 87. A tapped resistor 88 is inserted inthe plate lead of tube 81 for providing the appropriate division ofvoltage for condenser S7. This system of producing linearity incondenser charging rate is known in the related arts. Resistor 88 andcondenser 32 are temperature compensated.

When the second signal is delivered to flip-flop multivibrator 52, itreturns to its initial state, tube 81 again becomes conducting and theplate 81 returns to nearly ground potential. The stored charge oncondenser 82 is proportional to the time between arrival of the twosignals and this stored charge is trapped by diodes S3, and tube 89 inconjunction with resistor 84.

In the use of the circuit of Figure 3 in Figure 2 it is desirable thatthe rate of discharge of condenser 82 through leakage paths be decreasedin order to give more time for recording the condenser voltage atsubstantially the voltage to which the condenser had been chargedfollowing the occurrence of a fault. The delay in discharge isaccomplished by an amplifying tube 89 and a diode 90, connected as shownto resistor 84. When condenser 82 is being charged by the action of tubeSi the cathode of diode 83 is positive with respect to ground, makingthe upper end of resistor 84 positive with respect to its lower end andthe upper terminal of condenser 52 positive with respect to ground.Diode 90 in parallel with resistor84 permits current to flow in chargingcondenser 82 without being opposed by a severe voltage drop throughresistor 84.

In discharging condenser 82, diode 90 is non-conducting so that thedischarge current from condenser 8,2 makes the lower end of resistor 84positive with respect to the upper end. Amplifier tube 89 is biased by abiasing battery 91 to zero plate current when condenser 82 is notdischarging. When condenser 82 is discharging the development of adiiference of potential at the lower end of resistor 84, in respect tothe upper end, makes the control grid of amplifier tube 89 suicientlypositive in respect to the cathode thereof to permit the flow of platecurrent. Plate current flow in tube 89 increases the potential ofresistor 84 relative to ground and so retards the escape of current.Expressed in another way, it may be said that tube 89 provides a currentto ground in the leakage path followed by the current being dischargedfrom condenser 32. The leakage path is represented in Figure 3 by aresistor 92, shown as a broken line, across which, in effect, the platecurrent of tube 89 develops a voltage which would be the same as thatwhich would be iiowing if the voltage on condenser 82 were much higherthan it actually is. This' opposes the flow of current from condenser 32and, in consequence, delays the discharge thereof.

Reset switches, either ganged or independent, for the thyratron tubes 23and 53, electronic counter and the voltage storer may be provided foreither automatic or manual operation. These reset switches may beinterlinked with the circuit breakers in the substation to either causeor prevent reset as may be desired.

Although the descriptions given above would, in general, enable thoseskilled in this art to construct practical embodiments of our invention,a preferred form is illustrated in some detail in Figure 4. Figure 4corresponds to the schematic diagram in Figure l. The various resistorsand condensers and other conventional details shown in Figure 4 are notdescribed individuallyl insofar as they can be readily understood byreference to prior art. Amplifier 14, for example, is known in the artas a pulse amplifier or video amplier. Ampliiier l5, referred to as aphase splitter, is similar in principle to amplifiers known as phaseinverters or phase splitters used in audio amplification circuits. Fullwave rectifier 16 is analogous to a detector in an ordinary radiocircuit,

in this invention delivering pulses all of one polarity fron-r' an inputofV alternating polarity. Pulse amplifier I7 is similar in principle topulse5 amplifier I4 and ot similarly conventional design. inverteramplifier 11i-is a video-typ`e ampliiier that delivers pulsesof asinglepol' larity to' control thyratron switch tube 23a Cathode follower 19 isa conventionall circuit in which, however, the cathode-grid circuitresistance is only of the order of 1000 ohms. inverter amplier 21 isasimple' low-gain video amplifier.

Signal-biased amplifier is anala-gous i-n some respects to a volumecontrol in a conventional radioreceiver. In this invention, however, thesignal bias isV applied very rapidly and is retained only for a shorttime. The gain in amplifier 20 is set inversely in proportion to thesize of the signal delivered by cathode follower 19. The pulse signaldelivered by cathode follower 19 produces a voltage of brief durationacross a resistor 93. This voltage is impressed on a cathode-gridcoupling condenser 94. with a voltage consequently impressed on gridresistor 95. The voltage of resistor 95 is negative with respect toground and accordingly tends to' decrease gain in ampliiier 20.

ln order to be effective in this invention the time constant of thecircuit containing cathode resistor 93 and condenser 94 must be veryshort. This is accomplished by making resistor 93- low, of the order of1000- ohms and condenser 94 relatively small, of the order of 0.01microtarad. Condenser 94 discharges through the circuit' comprisingresistors 93` and 95. By making resistor 95 large, of the order of amegohm', condenser 94' discharges relatively slowly, taking time of theorder of 0.0i second. This length of timev is several times the durationof the cathode ray recording sweep. The essen tial requirement" is thatcondenser 94 charges very quickly and discharges comparatively slowly.

The synchronous motor-driven switch 38 includes the components numberedfrom 96 to 103 inclusive shown in Figure 4. An electric clock motor andcam 96 operate aV switch 97 periodically. T hyratron switch tube 23receives grid bias potential from -JC through grid resisters 9S and 99andV a stabilizing resistor 99'. The normal? bias voltage is maintainedon a condenser 101. Switch 97 is normally' open but closes briefly atpredetermined intervals. When switch 97 closes, the difference otpotential existing across a condenser 102 is impressed on the grid oftube 23 through resistor 98. Prior to closing switch 97, condenser 102has been uncharged, having been discharged through a resistor 103. Thuswhen switch 97 closes, resistor 98 is brought momentarily to ground?potential causing tube 23 to become conducting. The potential ofresistor 98 charges rapidly by condenser 1102 being charged throughresistors 99 and 100 to -C potential.

When tube 23 becomes conducting, a pulse of voltage is produced across acathode resistor 104 which is impressed on oscilloscope 22. Tube 23receives plate current from +B through coil 105 of relay 27. The surgeof plate' current in coil 105 operates relay 27 when tube 23 becomesconducting, operating camera 29, racking up one frame' of film. Themomentary surge of current through coil 105 is impressed on a neon orargon lamp 106 which is situated in the extension 34 of photographicshield' 3'1.

The' same voltage developed across coil 105 is impressed on the grid ofreset tube through grid resistor 107 causing tube 25 to draw a surge ofplate current through coil 108 of relay 26'. This opens the contacts ofrelay 26 interrupting the plate current of thyratron 23; By the timerelay 26 opens", condenser 102 will have become charged so that thepotential on the grid of tube 23 will have been restored to the normalnegative cutoff bias. When relay 2'6 closes, tube 23 will benoncon'ducting and the system will be ready for another operation.

Having described our invention, we claim:

l. ln the detection and location of power transmission line faults, themethod which consists of detecting fault surges at each end of saidline, initiating upon the arrival of a surge at one endi time recordingaction, transmitting from the other end of said line a radio impulseupon the arrival of a fault surge, receiving said radio impulse at saidone end of said line, recording the time elapsing between the detectionof said surge at said one end and the reception of said radio impulse,and computing therefrom the distance of said fault from the ends of saidline.

2. In the detection and location of power transmission li-n'e faults,the method as described in claim 2 in which, also, the transmission ofsaid radio impulse from said other end of said line is delayed after thearrival of a surge there by a length of time sufficient to assure thearrival at said one end of the line the surge received there over theline prior to the arrival, at said one end, of the radio impulsetransmit-ted' from said other end.

3. Incombinationl with an electrical transmission line, timing means,means coupled to' one point of said line and arranged to initiateoperation of said timing means on arrival of a pulse at said one point,radio transmitting means coupledv to another point of said line andarranged to transmit a radio pulse on arrival of a pulse at said otherpoint of said line, radio receiving means tuned to receive pulsestransmitted by said radio transmitter means and connected to said timingmeans and arranged to stop operation of said timing means on receipt ofa radio pulse.

4. The combination of claim 3 in which there are additionally providedmeans for introducing a delay in the transit time of pulse indicationbetween said other point and said timing means.

5. In combination with an electric transmission line, pulse generating'means coupled to one point of said line to provide, on the arrival atsaid one point of pulses of either polarity, a pulse of a certainpredetermined polarity, timing means connected to the output of saidpulse generating means, said timing means being arranged to have itsoperation initiated by said pulse of predetermined polarity, a pulsegenerating means coupled to a second point of said line and arranged toprovide, on the arrival at said second point of pulses of eitherpolarity, a pulse of a certain predetermined polarity, a radiotransmitter connecting to the output of said last-mentioned pulsegenerating means to convert the pulses supplied to the transmitter intoradio frequency pulses and to radiate said radio frequency pulsesthrough space, a radio receiver tuned to said radio frequency, theoutput of said receiver being applied to said timing device to stop itsoperation.

6. The combination of claim 5, in which means are provided to interposea delay between the arrival of said pulses of either polarity at saidsecond point and the input to said timing means from the radio receiver.

7. The combination of claim 5v, in which delay means is inserted by thesaid one point of said line and the pulse generator coupled thereto.

8. The combination of claim 5, in which the timing means is an electriccounting device.

9. The combination of claim 5, in which the timing device comprises ailip-iiop multivibrator receiving inputs from said pulse generatorcoupled to said one point, and from said radio receiver, the output ofsaid iiipflop multivibrator being connected to an electronic circuitarranged to provide a voltage increasing linearly with time undercontrol of said multivibrator, and a recording volt meter connected tosaid linear sweep voltage generator.

10. In combination with an electronic power line two channels coupled tosaid line at iirst and second points respectively, each of said channelsincluding a phase splitter for converting an applied pulsev into twopulses of opposite polarity, the output of said'` phase splitter beingconnected to a full wave rectifier for providing a pulse of apredetermined polarity, in the rst channel the output of said full waverectifier being connected to a first gas tube switch which in turn isconnected to an electronic counter and a dip-flop circuit, a radioreceiver connected through a second gas tube switch to 5 said electroniccounter and said Hip-flop circuit, the electronic counter being arrangedto have its operation started in response to the action of said firstgas tube switch and stopped in response to the action of the second gastube switch and at a different level in response to the 10 action of thesecond gas tube switch, the output of said flip-flop circuit beingconnected to a linear sweep and No references cited.

